Mongoose: How to sort aggregate response with two fields

Question

I have this mongoose query:

 MinutesSpentStudying.aggregate([
    { $match: { connected_user_id: ObjectId(user_id) } },
    {
      $project: {
        minutes_spent_studying: 1,
        year: { $year: "$date" },
        day: { $dayOfMonth: "$date" },
      },
    },
    {
      $group: {
        _id: {
          day: "$day",
          year: "$year",
        },
        total_minutes: { $sum: "$minutes_spent_studying" },
      },
    },
    { $sort: { _id: 1 } },
  ]);

It returns this response:

[
    {
        "_id": {
            "day": 2,
            "year": 2021
        },
        "total_minutes": 11
    },
    {
        "_id": {
            "day": 3,
            "year": 2021
        },
        "total_minutes": 1
    },
    {
        "_id": {
            "day": 26,
            "year": 2020
        },
        "total_minutes": 1
    },
    {
        "_id": {
            "day": 27,
            "year": 2020
        },
        "total_minutes": 3
    },
]

I'd like it to sort out by year, and then by day so that it returns the results of 2020 and then the result of 2021.

Any idea how to configure so as to achieve this result?

Answer 1

You can sort by multiple fields and use the dot notation for the nested ones:

{
    $sort: {
        "_id.year": 1,
        "_id.day": 1
    }
}

Mongo Playground